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Fire Extinguisher as a pressure vessel

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Fire Extinguisher as a pressure vessel

Unread postAuthor: evilvet » Tue Mar 29, 2011 10:34 pm

A question for those knowledgeable in this area.

I have a number of small (0.7kg to 2.0kg) fire extinguisher, B/E dry powder type and am considering them as tanks.

They are labeled as 100psi working pressure and 300psi max test.

In the spirit of the member whose tag is something like "your stupidity has no pressure rating", would running them regularly at 200psi be asking for something to go "boom" in close proximity to a currently attached body part ?

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Unread postAuthor: Zeus » Tue Mar 29, 2011 11:01 pm

I don't think 200PSI would be stupendously dangerous, if you're concerned and are happy to waste one, try hydro testing to failure.

Decide on an appropriate safety margin based on you results. Perhaps you assume the burst pressure of that tank is ~25% higher than the rest. Then a 1:3 ratio would be sensible, I'd leave it charged at that pressure for as long as possible, check for any bulging or weakening.

If all seems well, work at that pressure.

Also, I'd paint the inside to prevent rusting, you never know really.


saefroch's signature wrote:Always remember, your own idiocy has no pressure rating.
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Last edited by Zeus on Tue Mar 29, 2011 11:57 pm, edited 1 time in total.
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Unread postAuthor: Gippeto » Tue Mar 29, 2011 11:07 pm

I'd find a tank with a higher rating.

Check with a fire safety company...they're forever changing out old fire extinguishers. I get all the co2 I can use from my local guy for nothing....and it comes in a container rated for 1800psi. :wink: (Think I currently have ~ 40lbs) There are also dry chem extinguishers that have higher operating pressures (and thus ratings) than what you have.

It's junk to them...they're usually glad to get rid of it. Show 'em a cool (well built) launcher, and they'll likely be happy to help. Guys like cool toys...doesn't matter how old they are. 8)

"Stupidity has no pressure rating".....I like that. :)
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Working Pressure

Unread postAuthor: Technician1002 » Wed Mar 30, 2011 5:16 am

Working pressure is what the tank is designed to safely run. The test pressure is a stress test. If it passes, then the tank is considered safe at the working pressure. Repeated cycles above the working pressure may stress and weaken the tank. Tanks inflate somewhat with pressure and the stress can lead to stress cracks.

As mentioned by others, use a higher rated tank.
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Unread postAuthor: Crna Legija » Wed Mar 30, 2011 6:18 am

iv been using a dry chem tank for that past 2years at 300-500psi, i also welded a hinge on to it and im still fine. still stay at what you think it safe and allways do your own pressure test.

i filled the gun i had that tank connected to with water and put it in my 1000l water tank then filled it to 650psi it had lots of little leaks but dident blow up.

im looking for a new tank now because, its getting old and has started to rust. i want to get a soda stream bottle.
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